Mobile communication system, mobile station and diversity handover branch control method

Abstract

A handover method for controlling communication between a mobile station and base station(s) in a wireless communication system. The method includes measuring signal qualities transmitted from the base station(s), the measured signal qualities including a measured quality of a signal received from a certain base station; identifying the base station as an addition candidate based on the measured quality exceeding an addition threshold; thereafter detecting that the measured quality of the signal received from the addition candidate has further exceeded an active threshold which is greater than the addition threshold. The active threshold is determined in accordance with a quality of a signal transmitted from one or more active base stations. In response, the base stations are notified of information about the addition candidate; and a handover process is performed on the bases on this information.

1. A handover method for controlling a communication between a mobile station and at least one base station, in a wireless communication system including the mobile station and a plurality of base stations, said method comprising:
 an act of measuring qualities of signals transmitted from at least some of said plurality of base stations, the measured qualities of signals including a measured quality of a signal received from a certain base station; 
 an act of identifying the certain base station as an addition candidate based on the measured quality of the signal received from the certain base station exceeding an addition threshold; 
 after the act of identifying the certain base station as an addition candidate, an act of detecting that the measured quality of the signal received from the addition candidate has further exceeded an active threshold which is greater than the addition threshold, wherein the active threshold is determined in accordance with a quality of a signal transmitted from one or more active base stations; 
 in response to the act of detecting, an act of notifying one or more of the plurality of base stations of information about the addition candidate; and 
 an act of performing a handover process based on the information in the notification; 
 wherein the notification includes the measured quality. 
 
     
     
       2. A handover method according to  claim 1 , wherein the active threshold is based on at least the worst measured signal quality of the measured qualities of signals. 
     
     
       3. A handover method according to  claim 1 , wherein the notification is sent not at the act of identifying the certain base station as an addition candidate, but at the act of detecting that the measured quality of the signal received from the addition candidate has further increased to be higher than the active threshold. 
     
     
       4. A handover method according to  claim 1 , wherein said notification includes information indicative of precedence of at least some of the measured qualities of signals that correspond to one or more addition candidates. 
     
     
       5. A handover method according to  claim 1 , the method further comprising:
 transmitting information about a signal quality of base stations communicating with the mobile station. 
 
     
     
       6. A handover method according to  claim 5 , wherein the information includes information indicative of an order of precedence for the measured signal qualities of base stations communicating with the mobile station. 
     
     
       7. A handover method according to  claim 1 , wherein said act of performing the handover process adds a wired or fixed wireless branch between at least one base station and the addition candidate before commencing the transmission from the addition candidate.